The diagnosis system for storage battery aging status phenomena implemented up to this time is a system measuring the remaining capacity in a sample cell, by discharging the string of storage batteries in operation with full capacity or with necessary current, and by observing the voltage across the terminals as time changes. This method it is generally used in industries. The remaining capacity (life) of the storage batteries in the operating system can be diagnosed more accurately in comparison with the above method; but it is not suitable for finding out all the bad cells. A actual discharge method diagnoses the total remaining capacity of the storage battery string by grasping the capacity of only the minimum capacity unit cells among the battery string; therefore it is not suitable in finding all cells where the aging status is considerably progressed, and furthermore it requires a lot of manpower and expense to diagnose the aging status of the storage battery string in the charging state.
In order to check the healthiness of the storage batteries, the measuring instrument is commercialized to check the trouble of the storage batteries with the correlation of the terminal voltage and temperature while checking each cell by making use of the Lab View Program (Data analysis software) and Data Acquisition Card which are recently commercially sold, by measuring only the electrolyte temperature of each cell of the storage batteries and the voltage in floating charge and the charging current. With the above method the degree of progressed aging status can be grasped by comparing the terminal voltage of the unit cell in floating charge and the voltage of the cell in the same group of storage batteries in serial connection, but the variation of the terminal voltage is not small due to the amplitude of floating voltage and to the influence of the unit battery cell in serial or parallel connection, and there is no absolute correlation between the remaining capacity (aging status) and the terminal voltage in floating charge, the above method was thought doubtful about the reliability to adopt as a diagnosing method for the life or the healthiness of storage batteries.
The leading companies, YUASA in Japan and Polytronics in Canada, commercialized the instrument capable of measuring the internal impedance of storage batteries, since these instruments acquire the DC signal corresponding to the effective value of the internal impedance by synchronized waveform detection method with integrated semiconductor chip. When each string of the storage batteries which is in floating charge is manually measured, the internal impedance cannot be measured accurately because the AC voltage waveform is influenced by the charging ripple current. Furthermore, in case of analyzing the measured and stored data as a data base for systematic management of maintenance, the internal impedance is measured manually by moving the measuring lead to each terminal of the battery cells in floating charge. Therefore, there exists a risk of electric shock or a disadvantage of duplicated manpower and time to analyze the measured values. Additionally, the total data—surrounding temperature, gravity of electrolyte solution and charging current—necessary for diagnosis of aging status cannot be measured simultaneously. A few sample impedance measurements are easy but there is a great difficulty in accurate diagnosis of life from the simultaneous measurements of many cells.
The technology of “On-Line Battery Impedance Measurement”—U.S. Pat. No. 5,281,920, invented by John W. Wurst and et al on Jan. 25, 1994—was developed to diagnose the life of storage batteries, but the implementation method is completely different. This patent is composed of a voltage measurement module connected to a group of relay assemblies controlled by a system load controller, current measurement system and MPU. Impedance value is calculated by the decreasing speed value of the terminal voltage of the storage batteries discharged during 0.5 milli-sec and 20 milli-sec.